How the high temp limits in electric furnaces work. Part 3

Locating and checking operation of electric furnace limits.
This video is part of the heating and cooling series of training videos made to accompany my websites: and to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

29 Replies to “How the high temp limits in electric furnaces work. Part 3”

  1. Is a manual reset limit switch better from a safety point of view if my furnace doesn't have a thermal fuse?

  2. Had one of my thermal switches burn up and need to get a new one. How do you tell what temperature the limit switch should be. No mark or stickers on mine. I have seen 120-190. Also should I replace all four of them? Older Wesco Electric heater 960k. Says max air output 200 degrees with air intake 77

  3. Hi sir !
    I really appreciate yours video 😊!!
    I keep trying fix my furnace
    My furnace have limit switch whit a brass long contact 60t11 201728 c8730 l170 -40
    But I am not able to find one in my area I order 1 on internet
    My question is this limit switch have only to 2 contactor but not the long brass bracket can I replace whit a pieces of wires whit contactor both side and plug them to replace the fact it's missing the brass bracket ??

    Thank you very much for the answer !
    Have a good day!

  4. Hi…don't know if you're still responding to comments or not but I have an issue of my heat will not turn off even when AC is on. Duct work is great and a brand new thermostat installed since the issue started. Also clean filters….Does this sound like bad limit switches is the problem? Does this mean that they're "stuck closed"? Thank you for any info.
    Model FY4ANF036010AAAA


  5. my question is – the meanning L150–95 is temperature in F (in celsius it should be 65-35 C)? am i right?

  6. Wow- very interesting to see here- those high limit switch in terms of the temperature, absolutely awesome info to know in terms of how the heat works and the stages of heat.

  7. If the limits are bad and no fuse in the unit, will the building get fire? How does gas version work? Do you have a video on that? Thank you for your Great videos

  8. I have an electric fan coil system that has electric 5k elements. 208v the wire from switching relay to the electric element keeps burning. If it's not the wire then it's the relay coil. Using correct wire. What would cause the wires to keep burning ? could a bad temp limit switch do that?

  9. Im sure duds can be bought but what are the odds 2 brand new carrier limits being bad? On an electric 15kw unit only 1 strip works continuously. Narrowed problem to 2 bad limiters, ordered 2 new replacements online and having same issue, no matter their placement in the unit. I moved the one good old limiter around to test coils and it works flawlessly. The old bad ones and the replacements only work for a few seconds before tripping. around 90degrees.

  10. Having issues with my furnace blower has been replaced, circuit board, relays, thermostat. Not sure what else HVAC guy replaced still getting cold air. I noticed that there is a lot of rust buildup on the nuts that attach to the white part of the limit switch could this be the problem.

  11. Last year the blower stopped but the elements stayed on had to shut it off at the breaker.
    This year it blows lukewarm air . Did it burn up an element?

  12. Great videos sir! I'm having trouble with my electric furnace recently
    , it will sometimes only blow cold air. I have tested the continuity on all 3 limit switch and 1 of them looks to be always tripped even when cold. Is there a way I can bypass element/limit switch (#2of3) so only element 1 and 3 work. I can't change the limit switch right now, that's why I want my furnace to work like that temporarely. Thank you

  13. My heater in mobile home wont shut off when its reaches the set temp would this mean a bad limit switch?

  14. I have a Coleman Evcon EB15B that heats fine, but the cooling down fan won't turn off. I have replaced the thermostat and it's still doing it. Any suggestions??

  15. Hello Sir.I have a Coleman Eb15b furnace.When it's running the heat is like a cool warm and it runs all day but never reaches a temp of 75 in the mobile home.I have checked the sequences and the element and both are working fine.Can you tell me where would be a good point to look next.Thank you in advance

  16. I have an electronic trip furnace that will other come on. I replaced the thermostat and still furnace will not come on. I jumped the red and white wire still no heat. Fan functions in on position but not in auto position. Furnace fired up one time last night and shut off properly. It fired up again later but didn't blow any heat. Any suggestions? Thought it might be the heat elements but watching the video I am not sure. Thanks, Gary

  17. Another great demonstration video. Really enjoyed the "slow-mo" part of the safety switch opening up.

  18. I have an older Bryant 961-010 10kw electric furnace. It was operated with a clogged filter. I first replaced a limit switch that had failed. NO difference. The upper element had failed. the inline fuses are still OK so I have ordered a heating element kit. 2ea 5,000 watt strings.
    The limit switches appear to be the same but one is an L120-3-J6V and the other one is an R6V. Since they both open at 120, I'm assuming they're both really the same. It is just the position of the switch in the mounting plate that is different. Anyway, thanks for the video.

  19. should the high heat limit switch on my electric furnace be opening and closing? Should not the blower be producing enough air flow to keep it closed? Its a 2 speed blower…high and low speed…'s wired for high speed and it's heat only no AC…..

  20. I had a call that her furnace would shut off at night. To make a long story short. I ended up pulling the blower and cleaned off years of pack down dirt (it doesn't rattle anymore), and checked all sequencers, and limit switches, and I replaced 2/ 60 amp fuses. It's a Coleman 3500A series 15K.
    I don't understand why the blower has a 4 to 5 minute delay on an electric furnace. I've never worked on One that had a blower delay…………….is there a problem that I don't know about? ………….other than that the furnace works fine.

  21. i have switch limit L150-40f but i can find the same i find one whit L150-45f can i use that?

  22. TYVM for your excellent videos. Here's my EB23B story: I noticed that the laundry room was very hot. I felt the furnace door panel and it was hot. The fan was off. I lifted off the door and felt the squirrel cage fan housing and it was extremely hot. I turned off the breaker for the element and turned on the fan manually. The fan housing cooled off. My diagnosis (thanks to you) is I have a bad sequencer; one element is stuck on. Also, I must have a bad high-temp limit breaker switch because the element stayed on. How did I do?

  23. You don't clean flame sensors with emery cloth or sandpaper OO steel wool and you don't use needle nose pliers to tighten the HSI it puts unnecessary torque on it and it will snap use a nut driver nor a drill gun either.

  24. One of mine burned out. I got an extra limit switch from another air handler. Can i just use that one?

  25. My Intertherm furnace came with the 903906 15Kw element which has only 1 limit switch. A repairman replaced my element with a 9.6Kw element that has 2 limit switches. I want to use the original type of element again because it is much more efficient but I'm not sure how to connect the 1 limit switch. Could you please help me?

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